The present invention relates to a magnetic refrigerator comprising separated hot and cold heat exchange units wherein a heat transfer fluid that exchanges a heat with a magnetic heat exchange unit having the magnetocaloric material pieces arranged to have a gap therebetween separately circulates through a solenoid valve.
A conventional magnetic refrigerator is disclosed in U.S. Pat. No. 6,668,560. As shown in FIGS. 1 and 2, in accordance with the conventional magnetic refrigerator, while a heat transfer fluid 17 entering into a cold side inlet port 22 through a cold side inlet port pipe 21 flows to a hot side outlet port 34, the heat transfer fluid 17 absorbs a heat generated by a magnetocaloric effect of a magnetocaloric material 12 having a magnetic field applied thereto and exits to a hot side outlet port pipe 33 through a hot side outlet port ports 34 to cool the magnetocaloric material 12. A hot side sequentially passes the hot side outlet port pipe 33, a valve 71, a pump 60, and a hot heat exchanger 62 and flows into a magnetic heat exchange compartment 13. In a hot side inlet port pipe 31, the hot side is divided into the hot side inlet port pipe 31 and a cold side outlet port 23, and meets a cold side at a cold side outlet port pipe 24 and proceed to a valve 74. When the hot side moves from a hot side inlet port 32 to the cold side outlet port pipe 24, the hot side is cooled by passing the magnetocaloric material 12 already cooled by the hot side. The cold side that has passed through the valve 74 passes a cold heat exchanger 63 and flows to pipes 83 and 21 to repeat a cycle (a detailed description is omitted. See U.S. Pat. No. 6,668,560 for omitted reference numerals).
As described above, since the conventional magnetic refrigerator comprises twelve magnetic heat exchange compartments, four valves 71, 72, 73 and 74 and more than 24 pipes, it is difficult to manufacture the conventional magnetic refrigerator.
Moreover, since a single heat transfer fluid is circulated to serve as the hot side and the cold side simultaneously, that is, since the hot side enters at the hot side inlet port 32 to pass the cold magnetocaloric material (See FIG. 2) and cooled into the cold side to exit through the cold side outlet pipe 24, a efficiency of a heat exchange is degraded. It is known from this fact that when the heat transfer fluid having a temperature lower than that of the hot side entering the hot side inlet port 32 enters the hot side inlet port 32 and passes the cooled caloric material, the heat transfer fluid having a temperature lower at the cold side outlet pipe 24 may be flown out to improve the efficiency of the heat exchange.
In addition, since amount of the heat transfer fluid passing through the hot side cannot be controlled, a heat of the magnetocaloric material cannot be cooled promptly, thereby degrading the efficiency of the heat exchange.
On the other hand, since a fine mesh is used at the outlet port in order to prevent a problem that the magnetocaloric material of a power type is lost by the heat transfer fluid (coolant), the coolant cannot be circulated smoothly.
Moreover, since the coolant continues to pass the magnetocaloric material at the same spot, a smooth heat exchange is difficult.
In addition, a gadolinium having a microscopic size may be lost when the coolant enters or exits the magnetic heat exchange unit.